Winter weather has a definite effect on traffic; directly through decreased visibility, and indirectly through worse road conditions (for example, surfaces made slippery by snow, mud/slush or ice). The risk of accidents is multiplied. To reduce accident risk, and for safer and smoother traffic, a road weather information service was developed by the Finnish National Road Administration (Finnra) to assist in road maintenance and also to give a possibility to manage the traffic and inform the road users.
The information on the road weather and road surface conditions and the changes in the weather that influence the road surface conditions is obtained by the accurate road weather information and forecasts. The information is monitored on a 24-hour basis from each road district's road weather monitoring centre (RWMC). This allows better scheduling and choosing of maintenance measures, and optimizing the quantity of anti-icing to be applied.
Costs and benefits are of main interest when planning to invest to new monitoring systems, to the data management and traffic management tools and to the better information for the road users. Finnra has made studies of the costs and benefits regarding to the winter road maintenance and also regrading to the usefulness of the weather controlled road. Both of these studies show that there is a potential for the RWIS to be cost effective in these purposes. The method to analyse the costs and benefits was made in the project COST 309. The results concerning the Finnish road network were calcualted and they showed positive effect. The results obtained from the weather controlled road-experiment (1995), showed that using RWIS to manage the speed limits, gives significant effects to traffic safety. The investment costs for the whole experimental variable speed limit system were still too high that it would have been a profitable investment. It was, however, estimated that profitability will improve rapidly when the costs of the new technology decreases and the traffic amount will increase.